Emerging evidence suggests that chemokines play an important role at multiple steps during the induction of a pulmonary immune response, from the recruitment of dendritic cells (DC) to the lung, to the trafficking of antigen (Ag)-loaded DCs to the draining lymph nodes (LNs) to present the Ag to naive T cells. The receptors for certain chemokines such as MCP-1 (CCL2) and RANTES (CCLS) are highly expressed on immature DCs. RANTES was recently shown to induce cytokine and chemokine production in DCs. Our own preliminary studies show that both MCP-1 and RANTES influence lung DC function by modulating the expression of co-stimulatory molecules and cytokines in DCs and in the ability of DCs to induce the expression of subset-specific transcription factors such as T-bet (Th1-specific) and GATA-3 (Th2-specific) in CD4+ T cells. These observations are in line with previous reports that have implicated both MCP-1 and RANTES in lung inflammation. However, whether these chemokines can influence lung inflammation by modulating lung DC function and in turn T cell polarization in the local LNs has not been adequately explored at the present time. In this proposal, we will test the hypothesis that the chemokines MCP-1 and RANTES play important roles in lung inflammation by regulating DC function which in turn regulates T cell differentiation and function. To test this hypothesis we will: Aim I. Characterize the effect of the chemokines MCP-1 and RANTES on lung DC function. The effects of MCP-1 and RANTES on immature lung DCs will be studied by assessment of i) antigen uptake, ii) cytokine and chemokine expression, iii) expression of toll-like receptors (TLRs) iv) the induction of co-stimulatory molecules, and v) the induction of cell survival in the presence or absence of soluble antigen or toll-like receptor (TLR) agonists. Aim II. Determine the effect of the chemokines on lung DC function in vivo. Transgenic mice expressing MCP-1 or RANTES will be used to assess the effects of the chemokines on lung DC and T cell function in vivo. Mice will be subjected to a Th1- or a Th2-driven model of lung inflammation and the role of MCP-1 or RANTES will be determined using antagonists/neutralizing antibodies. Aim III. Investigate chemokine-induced signaling pathways in DCs and the influence of chemokine-treated DCs on T cell activation and differentiation. The role of specific signaling pathways in chemokine-modulated DC function will be studied. Also, the effect of chemokine-treated DCs on T cell responses will be determined at various levels including expression of T cell activation markers, activation of signaling pathways, expression of transcription factors and cytokine production.